Posterior surgical approach to the lumbar spine and its effect on the multifidus muscle

Study Design. This study investigated the changes in the lumbar muscles after posterior fusion of the lumbar spine and the potential correlation between muscular changes and the persistence of low back pain. Objectives. To evaluate prospectively the effect of the posterior approach to the spine on the lumbar erector spinae. Summary of Background Data. The posterior approach to the spine leads to considerable alteration of the erector spinae muscles. An eventual correlation between these changes and persisting pain or other clinical symptoms has not been investigated previously. Methods. Seventy-five patients undergoing spondylosyndesis for different indications (43 patients) or a second operation for the removal of internal fixation (32 patients) were allotted to the study. In each patient, four biopsy specimens from the lumbar multifidus muscle were harvested; in 14 patients, biopsies were taken at both operations. Size and distribution of the fiber types (I, IIA, IIB, IIC) were determined, and pain scoring (visual analogue scale) and the presence of neurologic deficits were recorded. Results. At the time of the first operation, 88% of the patients showed pathologic changes (altered internal structure, atrophy, type grouping) in one or more biopsies. Statistical analysis showed a correlation between both age and pain and type II (A + B) atrophy. After surgery, the patients showed significantly more biopsies with denervation signs than before surgery. No correlation could be made, however, between the intensity of pain before or after surgery and the relative number of biopsies with signs of denervation. Conclusions. Posterior surgery causes muscular alterations; however, no correlation with pain or other clinical symptoms could be established. Therefore, in the case of unsatisfactory results after surgery of the lumbar spine, reasons other than muscle damage caused by use of the posterior approach must be considered.